Why the usual clause fails
"No more than 0.0003 percent dead pixels" sounds precise. On a 40 square metre P2.5 wall that is about 2,400 dead pixels allowed, which is far worse than anyone would accept visually. The number is technically standard and practically useless.
What to specify instead
Three separate limits: total dead pixels on the whole wall, maximum dead pixels in any single module, and maximum in any single 100 × 100 mm area. A wall can pass the total limit and still have a cluster of eleven dead pixels in one module, which is exactly what an eye notices.
A workable set of numbers
| Parameter | Suggested limit |
|---|---|
| Total dead pixels | ≤ 0.0001 percent |
| Per module | ≤ 3 |
| Per 100 × 100 mm | ≤ 2 |
| Adjacent dead pixels | 0 |
The inspection method
Agree the method, not just the limit. Full red, full green, full blue, and full white, viewed from 1.5 m in normal room light, with the viewer moving across the wall. Some suppliers inspect in a dark room at 300 mm, which finds ten times as many and is not how the client will ever see it.
What happens when it fails
Replacement, credit, or rejection — choose one before you sign. The cheapest and most common is: the supplier ships replacement modules with the next order, and the client keeps them as spares. That avoids a service visit for a cosmetic issue.
The one thing to photograph
At acceptance, photograph the full-white wall in three sections at high resolution and keep the files. In year three, if a cluster appears, that photo tells you whether it arrived that way or developed later. With no baseline, every argument is a guess.